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OPA335 as Unity Gain Amplifier.

Other Parts Discussed in Thread: OPA335

I am using an OPA335 as a direct coupled Unity Gain Amplifier fed from a very small DC signal sensor and outputting through a cable to a connector. The purpose of the amplifer being to lower the output impedance and minimise noise pickup on the cable.

Witth zero input It seems to work very well when first switched on (outputting zero), but after about a minute gradually creeps up.

Is the problem caused by  being directly coupled without resistive buffers?

  • Roy,

    Are you using OPA335 in a single supply (0V, 5V) application?  If so, using OPA335 in unity gain with the input at the negative rail (0V) violates the voltage output swing specification (no linear op amp can swing at the output to negative rail): OPA335 output cannot swing closer than 50mV or 100mV above its negative rail with 100k and 10k load, respectively - see  PDS table below - thus driving it to ground will result in the output creeping up above ground.

    If you need further assistance, please include your circuit schematic as well as the input and supply voltages.

      

  • Thank you Marek, I am using a 3v rail, but will work on obtaining one or two volts below the negative rail and see if it solves my problem.